Fluid heater



I March 5, 1946. F. H. PRAEGER FLUID HEATER Filed Nov. 24, 1943 4 Sheets-Sheet l INVENTOR. FRANK H. PRAEGER.

' March 19466 F. H. PRAEGER 2,

FLUID HEATER Filed Nov. 24, 1945 4 Sheets-Sheet 2 8 00 f g\ g m INVENTOR.

BY FRANK H. FZAEGER. u:

March 5, 1946.

Filed Nov. 24, 1943 1 oooooooooooooooooooo F. H- PRAEGER' FLUID HEATER FILE-5.

4 Sheets-Sheet 3 FIG. 4.

INVENTOR.

FRANK H. PKAEGER.

March 5, 1946. F. H. PRAEGER 2,396,200

FLUID HEATER .Filed Nov. 24, 1943 4 Sheets-Sheet 4 Fue. 7

' INVENTOR. FRANK H. PzAaeeR'.

wan- 4 'zwwi Patented Mar. 5, 1946 FLUID HEATER.

Frank H. Praeger, Merion, Pa... assignor to Alcorn Combustion Company, Philadelphia, Pa., a corporation of Delaware Application November 24, 1943, Serial No. 511,758

13 Claims. (c1. 122-356) This invention, relating to the heating of fluids,

particularly hydrocarbon oil and its derivatives,'

has for an object the provision of a heater char.- acterized by the uniformity of its heat application and av flexibility in operation which makes possible the achievement of widely varying heating requirements.

.It has long been recognized that the heating of certain fluids such as petroleum and its derivatives presents a relatively difiicult problem. The stream of petroleum must not be overheated at any point during its travel through the heating tubes. If too much heat is applied to a limited portion of a tube, the oil film at that point is raised to a temperature where parasitic cracking ofthe hydrocarbon within the tube occurs, and carbon or tarry products are formed. Such i213.-

terial forms a deposit on the wall'of the tube. Any deposition on or within a tube lowers the rate of heat transfer and correspondingly increases the temperature of. the tube at that point. The

situation becomes progressively worse; the overheated portion becomes dangerously hot. The

foregoing phenomena have been recognized as a cause of shut-down and sometimes of tube failure. It is required that the heat generated within any fire chamber should be limited-to an amount such that there occurs a minimum of such "hot and excessive, and on all other points on the tube there would be no heat application. Hence the average rate of heat application to the tube would, be'exceedingly low and it would be of little value banks of tubes. After the gases have given up a part of their heat by radiation to the opposed banks of tubes, they are directed more and more toward the respective banks of tubes thereby to equalize the heat. application throughout the lengths of the tubes. The internal chimney greater stack effect is exerted omthe gases adjacent the floor and compensation is thereby pro-'- vided against the tendency of the gases to rise in the chamber proper. To accentuate this effect the space between the walls near the fioor may be greater than at the top thereof. This insures the flow from the fire chamber of approximately the same volume of gases per unitof area from the floor to the roof of the fire chamber.

' In a preferred form of the invention, the internal I chimney structure divides a heating chamber into as an emcient heating tube. as compared with one where heat is uniformly applied over the entire tube at the maximum permissible rate for the particular heating duty.

It is accordingly an object of the present invention to provide a heater in which the heat apstill-burning gases flow smoothly and evenly A plurality of vertically.

two fire chambers, provided with burners atopposite ends thereof. A plurality of said fire chambers may be disposed side by side each with its own internal chimney structure. A convection section common to the several fire chambers may be. located with its tubes extending at right angles to the vertical banks of horizontal tubes.

Other features and advantages of the invention will become apparent and will be presented in the following more detailed description, taken in con- Fig. .2 is a sectional elevation taken on the line 2-2 of Fig. 1;

Fig. 3 is a sectional elevation taken'on the line 3-3 'of Fig. 1;

Fig. 4 is a fractional view taken on 4-4 of Fig. 3;

Fig. 5 is a detailed view of a typical fuel burner and associated combustion chamber;

Fig. 6 is a horizontal sectional view of another embodiment of the invention; and" Fig. 7 is a sectional elevation taken on line 1--1 of Fig. 8. l

Referring to the drawings I have shown my invention in one form as applied to a multicell the line heater comprising a plurality of fire chambers lengthwise of the fire chamber and between the of a plurality of vertically disposed horizontal respective ends of the tubes of the bank 89 terminate within. header boxes 2i and 22, and the respective ends of the tubes 20 terminate within header boxes 23' and 24. The headers themselves are not shown but it is to be understood that headersare provided to connect the tubes in series or parallel for fiow of fluid therethrough.

As shown in Figs. 1 and 2 a plurality burner openings 26, spaced vertically one above the other, are located intermediate the tube banks is and 20 at one end 01' the heater; and a plurality of burner openings 27 are similarly located at the opposite end of the heater. As shown in Fig. each burner opening is provided with a fuel burner 28 which operates under the control of a valve 29 connected by a pipe 30 to a suitable source of fuel which may be either oil or gas or a combination of the two. Fuel projected by the burners through the burner openings, each preferably in the form oi a venturi for induction of air, is partially burned in mufiie or combustion chambers 38 and 32 respectively coextensive with the burner openings 26 and 27. By providing the relatively long and narrow vertically disposed muiiies 8i and 32, a column or a solid vertical stream of the still burning gases is directed outwardly and into the fire chambers i2 and it, and

there is little tendency for the gases to move from the column toward or to contact the sidewall tubes l9 and 20. The vertically elongated body of gases from the vertical and elongated rectangular muifies 3i and 32 moves centrally of the respective fire chambers 52 and it until it approaches the structure forming an internal fiue 83 This structure consists of walls 8 3 and 3b which extend toward each other and toward the elon-= gated muflle iii, the two walls at the juncture presenting an apex 36 directly opposite the mufiie iii. Similarly walls 3? and 38 form the apex 8t which is on a line with the elongated muifie 82. The

walls 36-455 and 87-38, Fig. 2, extend from the 7 bottom or fioor of the heater (is to the top or root 65. They are preferably made of a heat refractory material such as firstv quality fire brick. These walls are self-supporting. although additional steel supports may be included, if desired. Relatively short ends 01 the walls 3 3 and 3? extend parallel to the axes of the tubes l9 and approach each other to form a narrow opening 62 which is open and unobstructed from the bottom Similarly, like to the top-of the firechambers. ends of the walls 85 and 38 approach each other to form a like narrow opening it adjacent the tube bank 20. The outer faces of the walls 8% and serve two functions. They reflect heat toward the respective tubes i9 and 20 and thereby serve to equalize the intensity of the heat application. More particularly, it will be understood that as the gases travel from the elongated mufile 3! toward the central flue, the absorption of radiant heat by the vertical tube banks is and 20 lowers the temperature of the gases. The refiected radiant heat from the surfaces as and eb is applied to the tubes l9 and 2B in the zone or region where the heat application has been decreased and adds to the direct radiant heat received by these heat absorbing areas. The added radiant heat tends to equalize the heat application to tubes l9 and 20. The inclination of thewalls 34 and 35 not only controls the direction of the re-radlated heat but it also serves to divide the column oi combustion gases and gradually and increasingly deflects the gases into convecheat loss from the fire chambers 82 and is.

tion heat exchange with the tube surfaces in the region or vicinity of the openings 42 and 13. The superimposed convection heat transfer completes substantial compensation for the cooling of the combustion gases. As a result, substantial uniform heating of the entire lengths of the tubes of the banks i9 and 20 is achieved. The gases from the elongated muilles 8i and 32 after passage along the respective faces of the walls 341-35 and 8'i38 flow through the openings'M and 13 and into the internal flue provided by the space between the inner. faces of these walls. This space or the internal flue proper is subjected to stack draft in manner to be later explained.

As shown in Fig. 2, the fire chambers may be relatively high. By providing the internal chimney with the side openings 32 and it extending from the bottom to the top of the respective fire chambers, substantiailly uniform flow of the gases from bottom to top of the heater is achieved. The internal chimney itself produces a draft or a stack effect, which increases from the top to the bottom, being a maximum at the floor of the heater. The more highly heated gases in the respective fire chambers l2 and is will tend to rise, in contrast with the tendency of gases of lower temperature. This tendency of the hotter gases to rise and to flow along the upper part of the fire chamber is compensated for by the varying stack-draft applied to each fire chamber. In this manner, the combustion gases from the elonated mufies ill and 32 are caused to move in fairly well defined lines of flow through the center of the respective fire chambers l2 and ES, to divide around the projecting walls of the inner chimney 33 and evenly and uniformly to exit through the openings 32 and 613. The heat application to the tubes i t-fld is substantially entirely by radiation over'the larger part of the heat absorbing areas thereof, with the addition of convection heat as the gases are deflected by the walls of the inner chimney 38. The inner chimmy 83 with its side openings 62 and 33 provides the additional advantage of preventing radiant .ln many respects radiant heat may be compared with the behavior of light rays. If the openings 12 and 438 were directly opposite the burners or opened directly into the fire chambers i2 and i3 radiant heat would be radiated directly into the chimney s8 and a relatively large proportion thereof would appear in the convection section. Some of this radiant heat would be lost and that applied to the convection tubes would tend to overheat them. By providing the openings 32 and 33 adjacent the sidewall tubes is and 2B and at right angles to the direction of flow of the gases, they are so located as to minimize the loss of radiant heat. If the muilles 3| and 82 were considered as search lights it would be seen at once that very little light would enter the openings 42 and 68 whereas if they were located directly in the beam the full intensity of the light would be directed into them. In this respect, the action of the radiant heat is quite similar.

The walls 34-35 and 31-38 join the roof i'l as shown in Fig. 2. The roof itself is provided effect from' thenoor to the root, further to insure uniformity of flow of the gases across each fire chamber from the muiiies to the exit openings.

As already stated, a plurality of fire chambers lt-I'l have been illustrated in the embodiment of the invention comprising Figs. 1-4. Thus the fire chambers Iii and H are provided withthe internal'flue' M; the fire chambers l4 and It with an internal flue l8; and the fire chambers it and H are provided with an internal fiue 49 all of identical construction-with the flue 83 which has already been described at length. Directly above each of. the respective internal fiues, Fig. 4,

5t intoa bank of convection tubes 55, only one of which is shown in Fig. 3. Similarly, additional baiiies 56-459 distribute and guide the gases issuirig from the openings 4%, 5i and 52 so that they flow uniformly against and over the tubes of the convection bank b5. As shown in Fig. 2the tubes of the bankit may be spaced apart to a greater degree than the tubes of a second section We of the convection bank. The banks 55 and the are disposed at right angles to ,the

- 15 the staggered relationship is obviously unnecessary though it has been illustrated. The inclusion of the wall 15 also indicates that the present invention may be utilized in the construction of a heater consisting only or the fire chamber Iii and I1. With such a heater the common convection section would ordinarily be replaced; by an air preheater suitably connected to the burners; or by a small convection section; or a steam superheater may be utilized to lower the temperature of the combustion gases leaving the fire chamber corresponding to IE and I1.

With the foregoing understanding of the principles underlying the present invention, other modifications and embodiments will suggest themselves. For example, there has been indicated in the horizontal sectional view of Fi 6, the application of the present invention to a single end-fired heater in which still burning gases from burners 16 are by anelongated mufiie T8 'directed as a moving rectangular column of gases intermediate the vertical banks of horizontally disposed tubes Ti and it and toward deflecting baiiie structure it. prises self-supporting refractory walls having a rounded end 86 opposite the mufiie 1B, and sidewalls 65 and 82 which serve to maintain the combustion gases in contact with tubes W and 18 for a substantially longer time than is indicated in radiantly heated tube banks i5 and it and to the corresponding vertically disposed horizontal rows of tubes of the remaining fire chambers. Such a disposition of the convection banlr lends itself to economical construction without sacrifice of heating emciency; Eor example, the external duct it whioh'iorms the walls of the convection section is located directly above the respective internal flues. There is a minimum radiation loss and a minimum loss or draft. The arrangement as a whole is highly efiective.

Further structural features of the heater are indicated in conventional and partly diagram matic manner. The necessary trusses to support A the fire chambers proper. Moreover, the disposition of the convection bank below the roof of the heater tends to minimize radiation losses. I

the preceding embodiment of the invention. Instead of utilizing the space enclosed by the walls forming the structure Hi the internal flue in this embodiment of the invention is formed by a part of the end wall as and by a complementary wall at. Between the two semi-cylindrical sections or walls 83 and 3d a vertical internal flue B5 is provided. Vertical outlet passages lit and 88 are provided between the walls 83; and M, these passages extending from the bottom to slib-= stantially the top' of the heater. They lead into the internal flue 85. The flue til forms a part of a stack, the one being but a continuation or the other. Hence, the lower part lib of the builtin stack applies a stack draft, as described in connection with the preceding embodiment of the invention, to-the fire chamber.

In order to accentuate the compensating effect of the changing draft from the bottom to the top of the internal flue, the respective passages leading. to the internal flue may be tapered or wedge-shaped, with the base portion wider than the top. Such a wedge-shaped passage 88 is illustrated in Fig. '7, and the passage it is identical.

l Such wedge-shaped outlet openings at passages Again re'ierrlng'to-Flg. 1 it will be observed that between the adjacent fire chambers M and i6,- and i5 and il a heat refractory wall It is interposed. With the dividing wall it the rate 0! heating of the side-wall tubes is entirely indesuch as the double row of chambers ll and it are staggered so that opposite sides of each row of tubes receives radiant heat. There is heat application throughout the larger part 0! the circumferential area or each tube. with the wall provide constantly changing openings through which the gases pass into the internal flue or the built-in stack to. Though my invention in its several forms is not necessarily limited thereto, the inclination from the vertical of each side-wall of these openings or passages may be of the order of 0 degrees to 2 degrees.-

With heaters constructed as above described and explained, widely differing heating fluids such as gaseous hydrocarbons and heavy residuum may be heated according to any desired time-' temperature andpressure relations. The application of heat in each of the fire chambers ilk-ll, Figs. 1-4, may be at materially difierent rate than in the other fire chambers.

heated in each pair. of fire chambers. For example, the fire chambers l0 and II may be utiliced to heat a stream or oil to a temperature which will produce vapors. The derived vapors may then be superheated in the tubes of the. fire.

This baiile structure com- For other applications, diii'erent streams of petroleum may bechambers IZ-IIS, while the unvaporized oil may be simultaneously subjected to time and temperatures in the tubes of fire chambers l6 and H which will produce viscosity reduction thereof. In the heating of vapors it will be seen the present construction particularly adapts itself to the connection of a plurality of tubes in parallel one with the other. As will be best understood by those skilled in the art, the pressure drop may be reduced tremendously in this manner. The present invention leads itself to the use of conventional headers for connecting the tubes in parallel, in avoidance of specially designed headers whose first costs'and replacement costs may be very substantial.

What is claimed is:

l. A fluid heater comprising a plurality of horizontal tubes forming a pair of vertical banks spaced one from the other with a relatively long tube-free fire chamber therebetween, a plurality of burners spaced vertically one above the other for directing streams of combustion gases intermediate said banks of tubes and generally par allel to their longitudinal axes. means for producing equalized flow of gases from the bottom to the top of said chamber comprising internal chimney structure having an opening shielded zontal tubes forming a pair of vertical banks spaced one from the other to form therebetween a tube-free chamber relatively long as compared with its width, an' internal chimney structure disposed intermediate the ends of said chamber for dividing it into two fire chambers, said structure comprising refractory walls which from the bottom to the top of said chamber extend substantially across said chamber, said walls in the regions respectively adjacent said banks having a spacing between said walls for the flow of gases into the internal chimney structure in a direction generally at right angles to the axes of said from the view of said burners and through which i from the floor to the roof of said fire chamber said gases flow. and means connected to said chimney structure for applying a stack-draft thereto.

2. A fluid heater comprising a plurality of horizontal tubes forming a pair of vertical banks spaced one from the other with a relatively long tube-free fire chamber therebetween, a plurality of burners spaced vertically one above the other for directing streams of combustion gases intermediate said banks of tubes and generally parallel to their longitudinal axes, internal chimney structure spaced inwardly from said banks and extending from the floor tot-the roof of said fire chamber, said structure having narrow opentubes, and a plurality of burners at opposite ends of said chamber and spaced vertically one above the other for directing streams of combustion gases intermediate said banks of tubes, generally parallel to their longitudinal axes, and toward said internal chimney structure.

6; The combination as set forth in claim 5, in which said internal chimney structure comprises separate refractory wallsboth of which extend across the chamber and which approach each other in the regions adjacent said banks to form elongated openings from the bottom to the top of said chamber, and means cooperating with both of said walls to apply a stack-draft to the space between said walls.

7. A combination asset forth in claim 5, 'in which said internal chimney structure comprises separate refractory walls both of which extend across the chamber and which approach each other in the regionsadjacent said banks to form ings on opposite sides thereof which sides are I normal to the direction of flow of said gases, and which openings extend from the floor to the roof of said fire chamber, and means connected to said chimney structure in the region of said roof for applying a stack-draft thereto.

3. In a fluid heater haying a plurality of horizontal tubes forming a pair of vertical :banks spaced one from the other with a relatively long tube-free fire chamber therebetween, and a plu-' rality oi burners spaced vertically one above the other for directing streams of combustion gases intermediate said banks of tubes and generally parallel to their longitudinal axes, the combination of means for producing equalized flow of said gases from the bottom to the top of said chamber comprising internal chimney structure spaced inwardly from said banks and one portion of which extends toward said burners, said structure in a region adjacent each of said banks and generally at right angles to the axes of said tubes having an elongatedopening which extends from substantially the bottom to the top of said flre chamber for egress of gases from said fire chamber.

4. The combination as. set forth in claim 3 in which the openings on opposite sides of said chimney structure vary uniformly from a relatively. wide opening near the floor oi said fire chamber to a substantially narrower opening near the top of said ilre chamber, said openings being substantially in the form of tapering slots. 5. A fluid heater comprising a plurality of horielongated openings from the bottom to the top of said chamber, said openings being wider near the bottom of said chamber and progressively narrower toward the top of said chamber, and means cooperating with said internal chimney structure to apply a stack-draft to the space between said we s.

8. A fluid heater comprising a plurality of horizontal tubes forming a pair of vertical banks spaced one from thesother to form therebetween a tube-free chamber relatively long as compared with its width. internal flue structure intermediate the ends of said chamber and extending from the bottom to the top thereof, said structure comprising refractory walls which from positions ad- Jacent each other and one bank of said tubes respectively extend generally toward the opposite ends of said chamber and from positions midway of said chamber again extend toward each other to positions spaced one from the other and from the other of said banks thereby to form between 'said walls an internal flue, means connected to the regions where they approach each other, and

burners intermediate the respective ends of said chamber for directing combustion gases toward said internal flue and intermediate said banks of tubes.

9. A fluid heater comprising refractory walls, a floor and a roof, a plurality of vertical banks of horizontal tubes extending across said heater and forming therebetweena plurality of tubefree chambers which are relatively long as compared with their width, an internal chimney structure disposed intermediate each of said chambers, each of said structures consisting of a pair of walls which approach each other in the regions adiacent the two banks of tubes in each chamber for withdrawal of gases between said walls, a convection section disposed above and interconnecting said internal chimney structures, said convection section including a plurality of fluid-conducting tubes extending horizontally thereacross in directions generally normal to the direction of said first named banks of tubes and means for applying a stack-draft to said convection section and to said internal chimney structures.

10. A fluid. heater comprising a plurality of horizontal tubes forming a pair of vertical banks spaced one from the other with a'relatively long tube-free fire chamber therebetween, a plurality of burners spaced vertically one above the other for directing combustion gases intermediate said banks of tubes and generally parallel to their longitudinal axes, means for producing equalized flow oi gases from the bottom to the top of said chamher comprising a built-in stack, half of the lower part of which is formed by an end-wall of the heater, and the other half of which is formed by a second wall, said second wall cooperating with end-wall to form a narrow elongated openeatending from the bottom to the top of the heater and communicating with the upper part of said stack.

11. The combination as set forth in claim 10 in which said second wall cooperates with said end wall to form a pair of openings which extend from the bottom to the top of said fire chamber at opposite sides thereof and which respectively communicate with said stack.

12. The combination as set forth in claim 10 in which said second wall cooperates with said end wall to form a pair of openings of progressively narrower cross-sectional area from the bottom to the top of said fire chamber and which communicate with said stack, said openings being disposed at right angles to the direction of the flow of gases from said burners.

13. A fluid heater comprising a plurality of horizontal tubes forming a pair of vertical banks spaced one from the other with a relatively tubefree fire chamber therebetween, a plurality of burners spaced vertically one above the other, a vertically elongated combustion chamber of relatively narrow width compared with its vertical height for receiving combustion'gases from said burners and for directing them intermediate said banks of tubes and generally parallel to their longitudinal axes, means for producing equalized how of gases from said elongated combustion chamber upwardly and vertically through said chamber comprising internal chimney'structure having an opening shielded from. view of said burners and of a configuration such as to apply a greater stack-draft near the lower portion of said chamber than at the upper portion thereof,

for applying a stack-draft thereto.

FRANK H. PRAEGER. 

